1. Field of the Invention:
This invention relates to an exposure optical apparatus such as, for example, electrophotographic copying machine and the like, and is particularly concerned with improvement of a drive controlling means of the exposure optical apparatus.
2. Description of the Prior Art:
As is known generally, an exposure optical apparatus used on an electrophotographic copying machine has a document board moving type and a mirror carriage moving type, however, both the types have carriages driven and controlled generally on a wire pulley.
In such exposure optical apparatus as is controlled on the wire pulley, that of structure in which a carriage is controlled on two sets of wire pulleys disposed on both sides of a direction in which the carriage moves has been employed popularly of late in order to attain miniaturization and lightweight structure of the apparatus. FIG. 1 represents a conventional mirror carriage moving type exposure optical apparatus for which two sets of wire pulleys are employed, wherein a mirror carriage 3 with a first mirror 1 and an exposure lamp 2 mounted thereon and a half-speed carriage 6 with second and third mirrors 4, 5 mounted thereon are placed on rails 8A, 8B laid on both sides of a frame 7. The mirror carriage 3 and the half-speed carriage 6 are driven and controlled by two sets of wire pulleys 9A, 9B disposed on both sides of the direction rectangular to that in which the two carriages move. The wire pulleys 9A, 9B are provided with wires A, B with both ends connected to a stay on a fixed zone of the apparatus, the wires A, B being laid on driving pulleys 10, 11 of the half-speed carriage 6, moving end pulleys 12, 13 and a driving drum 14, coupled to both sides of the mirror carriage 3, thus reciprocating the mirror carriage 3 and the half-speed carriage 6 according to a rotating direction of the driving drum 14.
Accordingly, in such configuration of the wire pulleys 9A, 9B, not only directions in which the wires A, B are strained but also initial tensions of both the wires A, B relating to stretch thereof should be equalized to keep a parallelism among the mirrors 1, 4, 5 constant at all times and also to keep angles of the mirrors correct to a moving direction X at an arbitrary moved position.
In amplifying on a problem of initial tensions of both the wires A, B, assuming the wires A, B are strained in parallel with each other, then an influence due to initial tensions t.sub.a, t.sub.b of both the wires will be understood from obtaining both side positions of the mirror carriage 3 in case the mirror carriage 3 is drawn on a force F by both driving drums 14, 14. Let initial lengths of the wires A, B from the driving drums 14, 14 to the mirror carriage 3 be l.sub.a, l.sub.b, and a spring constant of both the wires A, B be R, then lengths L.sub.a, L.sub.b of both the wires A, B after deformation of the concerned part will be given: EQU L.sub.a =l.sub.a +(F=t.sub.a)/R EQU L.sub.b =l.sub.b +(F-t.sub.b)/R
Here, l.sub.a =l.sub.b under the state wherein the exposure optical apparatus has been framed and adjusted accordingly, therefore a condition for the mirror carriage 3 to move as keeping an initial parallelism of the mirror carriage 3 with the moving direction should be: EQU L.sub.a =L.sub.b
namely, EQU (F-t.sub.a)/R=(F-t.sub.b)/R (1)
As will be understood from Eq. 1, the initial tensions t.sub.a, t.sub.b of both the wires A, B must be set equally for keeping parallelism of the mirror carriage 3 which may exert a big influence on multiplication factor and focusing constant at all times.
The initial tensions t.sub.a, t.sub.b of the left and right wires A, B are therefore set equally hitherto by means of a spring balancer when the wires A, B are connected or by incorporating a tension roller 16 using a spring 15 controlled as illustrated midway of a route of the wires A, B. However, such means for adjsutment has a limit itself due not only to a solid difference between the wires A, B but also to a measuring precision of the spring balancer and a solid difference of the tension roller 16, thus involving a complicatedness and a long time for the adjusting work.